A biometric sensor device for attachment to the skin of a user comprises an electronic device (10) arranged to receive biometric signals or data from the user and a power cell (20) connected or connectable to the electronic device (10) for providing power thereto, the electronic device (10) and the power cell (20) being provided as discrete, thin, flexible parts connectable or connected together. Methods of construction of the device and applications for use of the device are also disclosed.
